Seal ring and associated method

ABSTRACT

An article is presented. The article includes a seal ring configured for use in an energy storage device, the seal ring comprising a first portion and a second portion that each include an alumina-based cermet, that comprises a sufficient amount of metal or metal alloy to be weldable, and the cermet comprises a ceramic material selected from a group consisting of silica, yttria, and ytterbia, and the seal ring further comprises a third region intervening between the first portion and the second portion that is sufficiently electrically insulative and of sufficient thickness to electrically isolate the first portion from the second portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 12/193,796,filed 19 Aug. 2008.

BACKGROUND

1. Technical Field

The invention includes embodiments that relate to a sealing material andseal ring for an energy storage device. The invention includesembodiments that relate to a method of sealing an electrochemical cell.

2. Discussion of Related Art

Development work has been undertaken on high temperature rechargeablebatteries using sodium for the negative electrodes. The liquid sodiumnegative electrode is separated from a positive electrode by asodium-ion conducting solid electrolyte. Suitable material includes betaalumina and beta” alumina, known as beta alumina separator electrolyte(BASE). Some electrochemical cells have a metallic casing. Interiorparts of the battery and the metallic casing may seal to interior partsof the battery. The ceramic parts of the cell can be joined via a sealglass. The seal glass may have undesirable characteristics associatedwith its use. Metallic parts can be joined by welding or thermalcompression bonding. Bonded parts formed from dissimilar materials in ahigh temperature cell may crack resulting due to thermal stress causedby mismatch in the coefficient of thermal expansion. The coefficient ofthermal expansion for a ceramic part and a metal part can be verydissimilar. The bond may have a limited life, and bond failure may causecell failure.

It may be desirable to have a sealing material for an energy storagedevice that differs from those sealing materials that are currentlyavailable. It may be desirable to have a seal structure that differsfrom those seal structures that are currently available. It may bedesirable to have a method of sealing an energy storage device thatdiffers from those methods that are currently available.

BRIEF DESCRIPTION

In accordance with an embodiment of the invention, an article ispresented. The article includes a seal ring configured for use in anenergy storage device, the seal ring comprising a first portion and asecond portion that each include an alumina-based cermet, that comprisesa sufficient amount of metal or metal alloy to be weldable, and thecermet comprises a ceramic material selected from a group consisting ofsilica, yttria, and ytterbia; and the seal ring further comprises athird region intervening between the first portion and the secondportion that is sufficiently electrically insulative and of sufficientthickness to electrically isolate the first portion from the secondportion.

In accordance with an embodiment of the invention, an energy storagedevice having a metal housing is presented. The energy storage deviceincludes a cathodic material comprising a metal halide in communicationwith an ion-conductive and electrically-insulative separator, and thecathodic material forms an ion capable of being conducted through theseparator, a seal ring comprising a first portion sealed to the metalhousing, and another portion electrically isolated from the firstportion and that is sealed to the cap, and the seal ring is resistant tocorrosion or degradation by contact of a reaction product of the metalhalide formed during operation of the energy storage device.

In accordance with still another embodiment, a method is presented. Themethod includes the steps of forming a seal ring having an electricallyconductive first portion and an electrically conductive second portionthat is separated from the weldable first portion by an electricallyinsulating intervening portion.

BRIEF DESCRIPTION OF DRAWING FIGURES

FIG. 1 is a cross sectional side view schematic of an article accordingto one embodiment of the invention.

DETAILED DESCRIPTION

The invention includes embodiments that relate to a sealing material anda seal ring for an energy storage device. The invention includesembodiments that relate to a method of sealing an electrochemical cellin the energy storage device.

As used herein, cathodic material is the material that supplieselectrons during charge and is present as part of a redox reaction.Anodic material accepts electrons during charge and is present as partof the redox reaction. A monolith is a single block or piece, asdistinguished from a part made by fusing or bonding multiple blocks orpieces together.

The term weld is used to unite or fuse (as pieces of metal) by heat orcompression. For ease of illustration, unless indicated otherwise bylanguage or context the term “weld” includes thermal compressionbonding, soldering, and brazing, in addition to the traditional meaningof weld. For the weld, suitable energy sources can include a flame,plasma, an electric arc, a laser, an electron beam, friction, RF andultrasound. In one embodiment, the weld coalesces the parts to bejoined. Coalescence occurs where two or more pieces of weldable materialare bonded together by liquefying the places where they are to bebonded, flowing these liquids together, and allowing the liquid tosolidify. At the end of the coalescence process the two pieces havebecome one continuous solid.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it may be about related. Accordingly, a value modifiedby a term such as “about” is not limited to the precise value specified.In some instances, the approximating language may correspond to theprecision of an instrument for measuring the value.

In accordance with an embodiment of the invention, an article isprovided that includes a seal ring for an energy storage device. Theseal ring includes a weldable first portion and a weldable secondportion. The weldable first portion and the weldable second portion areelectrically isolatable from each other by an electrically insulatingthird portion. In one embodiment, the seal ring is a monolith.

The weldable first portion and the weldable second portion can bedefined by composition and/or function. The weldable first portion doesnot need to have the same composition as the weldable second portion. Ininstances where the weldable first portion seals to a part that differsfrom a part to which the weldable second portion seals, the weldableportions may differ in composition from each other. In one embodiment,the weldable first portion and the weldable second portion may have thesame cermet, that is, the same ceramic-metal composition. In oneembodiment, the weldable first portion and the weldable second portionmay include different cermets. The compositions of the cermet for theweldable first portion and the weldable second portion may differ interms of the type or amount of ceramic material present in the cermet,the type or amount of metal present in the cermet, and the proportion ofthe metal to the ceramic present in the cermet.

On the seal ring, the function relates to the ability to weld orcompression bond to a mating surface. With regard to the composition,the seal ring includes a cermet that defines the boundaries of theweldable first portion and the weldable second portion. Cermet is acomposite material composed of a ceramic and a metallic material. Thecermet properties depend on such factors as the individual properties ofthe ceramic and of the metal, the amount and the relationship of theceramic to the metal in the cermet composition, and other factors.

The ceramic material of the cermet may include one or more of alumina,silica, yttria or ytterbia. Suitable alumina may be in the form ofsingle crystal sapphire or micrograin polycrystalline alumina (μPCA).The silica may be in form of garnet. Other suitable mixtures ofmaterials or forms may include spinel, yttrium-aluminum-garnet,ytterbium-aluminum-garnet. In one embodiment, the cermet ceramicmaterial consists essentially of only one of micrograin polycrystallinealumina (μPCA), yttrium-aluminum-garnet or ytterbium-aluminum-garnet. Inone embodiment, the ceramic material consists essentially of alumina.

A suitable cermet may include a refractory metal disposed in definedportions or zones. Suitable refractory metals may include those thatallow for welding. Examples of suitable refractory metals may includeone or more of molybdenum, rhenium, tantalum or tungsten. In oneembodiment, the cermet may include only one of molybdenum, rhenium,tantalum or tungsten. In one embodiment, the cermet may include two ofthe refractory metals selected from molybdenum, rhenium, tantalum ortungsten. The cermet may include a refractory metal that consistsessentially of tungsten. The cermet may include a refractory metal thatconsists essentially of molybdenum.

The cermet weldability performance in the weldable first portion and theweldable second portion may depend at least in part on the type andamount of the refractory metal present. The proportion of the refractorymetal in the cermet may be less than about 90 volume percent. In oneembodiment, the proportion of the refractory metal in the cermet may bein a range of from about 100 volume percent to about 50 volume percent,from about 50 volume percent to about 45 volume percent, from about 45volume percent to about 35 volume percent, from about 35 volume percentto about 30 volume percent, from about 30 volume percent to about 25volume percent, from about 25 volume percent to about 20 volume percent,from about 20 volume percent to about 15 volume percent, from about 15volume percent to about 10 volume percent, from about 10 volume percentto about 5 volume percent, or from about 5 volume percent to about 1volume percent. In one embodiment, the proportion of the refractorymetal in the cermet may be less than about 1 volume percent.

Optionally, the weldable first portion and/or the weldable secondportion each may include a unidirectional functionally graded cermet.The functionally graded cermet is a composite of a ceramic and a metalin which the proportion of the metal to ceramic changes as a function ofdistance in one direction. Control over the proportion or ratio of themetal to the ceramic provides control over properties of thefunctionally graded cermet. Such properties include one or more ofcoefficient of thermal expansion (CTE), poison's ratio, elastic modulus,crack resistance, impact resistance, electrical conductivity, oxidation,dross, slag, thermal stability, chemical resistance, melt temperature,weldability, and the like. Further, in one embodiment, the weldablefirst portion and/or the weldable second portion each may include abi-directional functionally graded cermet. In such an embodiment, theproportion or ratio of the ceramic to the metal changes as a function ofdistance in two different directions. The proportion or ratio changeover distance may be continuous and uniform over the distance, may becontinuous and accelerating or decelerating over the distance, or may bea step function having discrete segments of substantially non-changingproportion or ratio.

The compositions of the cermet for the weldable first portion and theweldable second portion may be selected to minimize or eliminate thermalstress. The thermal stress may be due to coefficient of thermalexpansion mismatch among different components of the device. A higherproportion of the refractory metal in the weldable portions may bewelded relatively easily to other metallic components or parts.

In one embodiment, the weldable portion or zone includes steel.Stainless steels or corrosion-resisting steels are a family of iron-basealloys having relatively high resistance to corrosion. These steels donot rust and resist attack by many liquids, gases, and chemicals. Manyof the stainless steels have good low-temperature toughness andductility. Most of them exhibit good strength properties and resistanceto scaling at high temperatures. All stainless steels contain iron asthe main element and chromium in amounts ranging from about 11 percentto about 30 percent. Chromium provides the basic corrosion resistance tostainless steels. In one embodiment, the weldable portion or zoneincludes nickel, and may consist essentially of nickel.

Selection of metal(s) for use in weldable portions may include referenceto the mating weld surface. In one embodiment, the mating weld surfaceis chromium-nickel stainless steel. While other mating weld surfaces arecontemplated, stainless steel is discussed here as an example of metalselection considerations. In one embodiment, iron and nickel content inthe weld structure may be controlled to affect the thermal conductivityand the electrical conductivity. The chromium-nickel steels belong toAISI/SAE 300 series of stainless steels, which may be selected withreference to the above-identified criteria. The stainless steel matingsurface may be nonmagnetic and have a controlled grain size, grainorientation, or microstructure, such as austenitic or martenstiticmicrostructures. Weldable portions or weldable zones may be formed tomatch the properties, composition and characteristics of thecorresponding mating surface to which it is to be welded.

Manganese may be added to some of the weldable portions. Nickel may bereplaced by manganese, possibly in a two-to-one relationship. Withregard to the housing, the AISI/SAE 200 series of stainless steels arethe chromium-nickel-manganese series, and these steels have anaustenitic microstructure and they are nonmagnetic. Molybdenum may beincluded in the weldable portions. Molybdenum may improve the creepresistance at elevated temperatures, and may increase resistance topitting and corrosion.

The weldable first portion may contact a first pole and the weldablesecond portion may contact a second pole of the energy storage device. Apole is an electrode of the device. The first pole of the energy storagedevice may be positive and the second pole may be negative.

The electrically insulating third portion electrically isolates theweldable first portion from the weldable second portion. The thirdportion may physically separate the anodic material from the cathodicmaterial. The third portion may include or be formed from anelectrically insulating material. Suitable material for use aselectrically insulating material may include alumina. The dielectricstrength of the material in the third portion or zone is greater thanthe voltage or current potential differential between the anode andcathode material. If a lower dielectric constant material is used, thewidth of the third zone may be selected to be larger—and the reverseconfiguration is available. In one embodiment, the third zone or portionhas the composition and properties listed in Table 1.

TABLE 1 third zone properties PROPERTY UNITS OF MEASURE VALUE Densitygm/cc    3.89 Porosity %  0 Flexural Strength MPa (lb/in² × 10³) 379Elastic Modulus GPa (lb/in² × 10⁶) 375 Shear Modulus GPa (lb/in² × 10⁶)152 Bulk Modulus GPa (lb/in² × 10⁶) 228 Poisson's Ratio —    0.22Compressive Strength MPa (lb/in² × 10³) 2600  Hardness Kg/mm² 1440 Fracture Toughness K_(IC) MPa · m^(1/2)  4 Maximum Use Temperature ° C.1750  (no load) Thermal Conductivity W/m ° K  35 Coefficient of Thermal10⁻⁶/° C.    8.4 Expansion Specific Heat J/Kg · ° K 880 DielectricStrength ac-kv/mm   16.9 Dielectric Constant @ 1 MHz    9.8 DissipationFactor @ 1 kHz     0.0002 Loss Tangent @ 1 kHz — Volume Resistivity ohm· cm  >10¹⁴

In one embodiment, the seal ring for the device may include a fourthportion. The fourth portion may secure to the ion-conductive separator.The fourth portion may be formed from a material selected to have acoefficient of thermal expansion matching with that of theion-conductive separator. The fourth portion may include a modifiedalumina. As a coefficient of thermal expansion of modified aluminafourth portion may match that of an ion-conductive alumina separator,the fourth portion of the seal ring may protect the seal ring as well asthe ion-conductive alumina separator from cracking induced due tothermal stress.

The weldable first portion, the weldable second portion, theelectrically insulating third portion and the optional fourth portionwithin the seal ring may be oriented or located relative to each otherto minimize thermal stress during operation and heating of the sealring. The fourth portion may be juxtaposed to the weldable secondportion to an opposite side of the third portion.

With reference to FIG. 1, an energy storage device 100 includes ahousing 102. The housing is cylindrical and has an outward facingsurface 104 and an inward facing (or “inner”) surface 106. The housinginner surface defines a device volume 108. The housing has a sealablefirst end 110. The housing first end has a peripheral edge (no referencenumber provided) that defines an opening or aperture 112 in the housing.An insert component system 114 is disposable in, and able to seal, thehousing aperture. The insert component system includes a cap 120, acurrent collector 122, and a seal ring 124.

The cap interacts with the current collector to allow for electricalcoupling of the current collector to outside of the energy storagedevice. The cap is secured to the seal ring in such a manner asdiscussed in further detail hereinbelow. The current collector extendsinto the housing volume. An electrically insulative and ionicallyconductive separator tube 130, within the housing volume, defines twoelectrically isolated compartments—an anode compartment 132 and acathode compartment 134, which are arranged in the illustratedembodiment as shown. More particularly, the separator has an inwardfacing surface 140 that defines the cathode compartment, and an outwardfacing surface 142 that defines the anode compartment. The currentcollector, then, extends into the cathode compartment within the housingvolume.

The seal ring is a toroid in the illustrated embodiment and has an innersurface 150 that defines a seal ring aperture 152 through which thecurrent collector extends. A housing weld structure 154 secures the sealring to the housing inner surface proximate to the housing first end. Acap weld structure 156 secures the seal ring to the cap.

The seal ring is a monolithic structure that has a plurality ofcompositionally and/or functionally definable zones. With reference tothe seal ring shown in FIG. 1, there are three zones. An electricallyinsulative zone 160 extends through the seal ring body to electricallyisolate a first weldable zone 162 from a second weldable zone 164. Whilethe defining line between the zones appears as a step function change inthe illustrated embodiment, in some other embodiments a transitionsub-zone may be interposed between the zone interfaces where thecompositional ratio or gradient changes as a function of location ordistance. The first weldable zone secures to the housing inner surfacevia the housing weld structure. The second weldable zone secures to thecap via the cap weld structure. A cathode material can be added throughan aperture, is not shown.

The metal content in the first and second weldable zones differs fromeach other in both amount and type. It is noted that in otherembodiments, one or both of the metal type or amount may be the same.The housing in this instance is stainless steel, and the first weldableportion includes metal that matches the composition and properties ofthe housing. The cap in this instance is majority nickel in a nickelalloy. The second weldable portion includes metal that matches thecomposition and properties of the cap and the insert component system.

A separator seal structure 170 secures the seal ring to the separator.In this embodiment, the separator seal structure is a glassy material.Further, while relating specifically to the illustrated embodiment, theseparator seal structure contacts and secures to the seal ring overportions of both the second weldable zone and the electricallyinsulative zone. In this configuration, the glassy material is selectedto be electrically insulative and chemically resistant in the operatingenvironment. Other considerations, such as glass transition temperatureand thermal expansion coefficient may be taken into account for materialselection.

With regard to welding the weldable portion to the mating surface arcwelding, friction welding, laser or directed energy welding, ultrasonicwelding, and gas welding may be used depending on the processspecifications. For arc welding, a welding power supply creates andmaintains an electric arc between an electrode and the base material tomelt the target material at the welding point or welding line. The arcwelder can use either direct (DC) or alternating (AC) current, andconsumable or non-consumable electrodes. Flux may be present in someembodiments. A blanket of inert or semi-inert gas, known as a shieldinggas, may protect the welding region, and filler material may be used.Electron beam welding (EBW) is a fusion welding process in which a beamof high-velocity electrons is applied to the materials being joined. Theworkpieces melt as the kinetic energy of the electrons is transformedinto heat upon impact, and the filler metal, if used, also melts to formpart of the weld. The welding may be done under vacuum to preventdispersion of the electron beam.

In one embodiment, the weldable portions may be amenable to thermalcompression bonding, which is a cermet-to-metal seal involving amismatch of the thermal expansion rates of the materials used. Duringthe cooling stage, after the firing process, the outer member forms adiffusion bond to the ceramic. The compressive forces created result inhermeticity.

EXAMPLES

Unless specified otherwise, ingredients are commercially available fromsuch common chemical suppliers as Aldrich Chemical Company (Milwaukee,Wis.).

Example 1 Forming a Seal Ring

A cylindrical pressing form is filled with a suspension of cermet(alumina, refractory metal) particles made with polyvinyl organicbinder. A piston presses and forms the suspension at an elevatedtemperature to form a first green portion that will ultimately form thefirst weldable portion. A uniaxial press with a pressure of 40 ksi isapplied. After the piston is withdrawn, a second suspension is filledinto the form in contact with the first green portion. The secondsuspension includes electrically insulative alumina powder and PVAbinder. The piston presses and heats the intermediate component to forma second green portion. After the piston is withdrawn, a third cermetsuspension (with binder and refractory metal powder) is filled into theform in contact with the second green portion. The metal content of thefirst and third suspensions is sufficient to allow for weldingsubsequent to manufacture. Particularly, the first suspension has about50 percent by weight of metal relative to the alumina, and the secondsuspension has about 60 percent by weight of metal. The placement of thesuspension materials relative to each other is selected based on thestructural requirements of the end seal ring. In this instance, thethird suspension does not contact the first green portion. The pistonpresses the third suspension at an elevated temperature.

The compacted cermet green structure is removed from the mold. Thecompacted cermet green structure is prefired at 1200 degrees Celsius. Asneeded, post press machining is performed. The prefired seal ring issintered, in hydrogen, at a temperature of about 1800 degrees Celsius.For comparison, the experiment is repeated, but the sintered seal ringfurther is hot-isostatically-pressed at 2000 degrees Celsius to producea fully dense body.

Example 2 Sealing an Energy Storage Device

A seal ring is formed as disclosed in Example 1. The seal ring issecured to a separator via a glass seal to form a seal ring assembly.The seal ring assembly is disposed in an energy storage device housing.A cap with a current collector is inserted into the seal ring apertureso that the current collector is in contact with a cathode fill materialthat is inside the separator. Alternatively, a ring or bridge piece witha current collector is inserted into the seal ring aperture. In a singlesubstantially continuous process, the first and second weldable portionsof the seal ring are welded to the housing inner surface and to the cap,respectively. The cathode materials can be added through the aperture inthe bridge piece. The cap is then welded to the bridge piece. Theweldable portions flow and seal with their respective mating surfaces toform a hermetic weld structure.

Example 3 Sealing an Energy Storage Device

A seal ring is formed as disclosed in Example 1. The seal ring is weldedto the inner surface of the can using an arc welding process. Inparticular, a tungsten inert gas (TIG) welding process is used. Cathodematerial is filled into the separator inner volume. A cap is placed overthe seal ring aperture to contact another weldable portion of the sealring. The cap is welded to the seal ring using either the TIG process orthe Plasma Arc Weld method (PAW). The energy storage device produced asin this example allows for the pre-production of the housing, seal ring,and separator sub-component. It is noted that other minor components ofthe energy storage device have been omitted for clarity. Such componentsmay include a support shim for the separator, a wick for the anodematerial, and the like. These listed components may be disposed in ananode chamber, and pre-production approaches, such as in this example,may allow for increased productivity and/or increased protection forthose pre-packaged components.

The embodiments described herein are examples of articles, systems, andmethods having elements corresponding to the elements of the inventionrecited in the claims. This written description may enable those ofordinary skill in the art to make and use embodiments having alternativeelements that likewise correspond to the elements of the inventionrecited in the claims. The scope of the invention thus includesarticles, systems and methods that do not differ from the literallanguage of the claims, and further includes other articles, systems andmethods with insubstantial differences from the literal language of theclaims. While only certain features and embodiments have beenillustrated and described herein, many modifications and changes mayoccur to one of ordinary skill in the relevant art. The appended claimscover all such modifications and changes.

What is claimed is:
 1. An article, comprising: a seal ring configuredfor use in an energy storage device, the seal ring comprising a firstportion and a second portion that each include an alumina-based cermet,that comprises a sufficient amount of metal or metal alloy to beweldable, and the cermet comprises a ceramic material selected from agroup consisting of silica, yttria, and ytterbia; and the seal ringfurther comprises a third region intervening between the first portionand the second portion that is sufficiently electrically insulative andof sufficient thickness to electrically isolate the first portion fromthe second portion.
 2. An energy storage device having a metal housing,comprising: a cathodic material comprising a metal halide incommunication with an ion-conductive and electrically-insulativeseparator, and the cathodic material forms an ion capable of beingconducted through the separator; a seal ring comprising a first portionsealed to the metal housing, and another portion electrically isolatedfrom the first portion and that is sealed to the cap, and the seal ringis resistant to corrosion or degradation by contact of a reactionproduct of the metal halide formed during operation of the energystorage device.
 3. The energy storage device as defined in claim 2,wherein the seal ring further comprises an electrically insulative thirdportion disposed between the first portion and the metal content of theseal ring depends on the location in the seal ring such that the thirdportion has relatively less non-oxide metal content than other portionsof the seal ring, and the rate of change of the metal concentration fromat least one seal ring portion to another seal ring portion is gradualto form a concentration gradient radially across the seal ring.
 4. Theenergy storage device as defined in claim 2, wherein the cathodicmaterial comprises one or more metals selected from the group consistingof copper, chromium, iron, nickel, and zinc.
 5. The energy storagedevice as defined in claim 2, wherein the cathodic material comprisesone or more halides selected from the group consisting of chlorine,fluorine, bromine, and iodine.
 6. A method, comprising: forming a sealring having an electrically conductive first portion and an electricallyconductive second portion that is separated from the weldable firstportion by an electrically insulating intervening portion.
 7. The methodas defined in claim 6, further comprising sealing an energy storagedevice with the seal ring by securing the first portion to a metalhousing of the energy storage device, and securing the second portion toan inner component of the energy storage device.
 8. The method asdefined in claim 7, wherein sealing comprises welding or thermalcompression bonding.
 9. The method as defined in claim 8, whereinwelding comprises ultrasonic welding, arc welding, or energy beamwelding.
 10. The method as defined in claim 8, wherein welding comprisesbrazing.
 11. The method as defined in claim 7, further comprisingsecuring a fourth portion of the seal ring to an ion-conductivealumina-based separator disposed within the metal housing.